A low temperature poly-silicon (briefly called as LTPS) thin film transistor display device differs from a traditional amorphous silicon thin film transistor display device in that, its electronic mobility can reach 50 to 200 cm2/vs, and then the channel area can be reduced effectively so as to decrease the area of a thin film transistor device, and to achieve an object of improving the aperture ratio and the degree of integration. As a result, while the brightness of the display is improved, the power consumption can be reduced as well.
In the LTPS process, in order to reduce the line resistance, each signal line is generally made by using metal aluminum (Al) with relatively low cost, relatively high conductivity and very small metal ion diffusion property. However, when a subsequent Hydro (hydrogenating) process is carried on, due to the thermal expansion property of pure aluminum itself, a phenomenon of small protrusion (hillock) on surface is very prone to occur to pure Al with a relatively high thickness in the event that grain directions are relatively consistent. Consequently, the contact situation of signal lines and the follow-up optical inspection work are affected greatly.